1. Field of the Invention
The present invention relates to a light transmitting plate holding construction of an image forming device. More specifically, it relates to a holding construction of an optical filter or a dust-proof glass plate of an optical system projecting an image information on a photosensitive body.
2. Description of the Prior Art
An image forming device, for example, an electrophotographic copying machine usually utilizes fine particle toner as a developing agent. The toner is so fine and light (e.g. a particle diameter is 5-30 .mu.m and its apparent density is 0.3-0.4 g/cc) that it tends to float inside the copying machine and adhere to each part.
Meanwhile, a light transmitting plate such as an optical filter or dust-proof glass plate may be used in an optical system projecting an image information on a photosensitive body of the image forming device, (e.g. refer to U.S. Pat. No. 4,549,803). Such a light transmitting plate is always exposed to adhesion of the toner, which is an obstacle to the projection of the image information, results in difficulty in accurate copying.
As a countermeasure thereto, it has been proposed to attach means for protecting against adhesion of the toner on the light transmitting plate (see U.S. Pat. No. 4,469,430). That is, a lens as the light transmitting plate is mounted by fixing a clamp member on a lens holder by means of screws, and the clamp member is provided with a dust-proof box removable in a sliding fashion so as to cover only one side of the lens. The dust-proof box is able to remove the toner before it adheres to the lens by the magnetic attraction force of the magnet, thereby reducing adhesion of the toner to the lens. However, since the dust-proof box covers only one side of the lens, it is difficult to totally seal between each part (e.g. between the lens holder and clamp member or the clamp member and dust-proof box) against the fine dust because such parts are very elongated. Thus, in particular, when a great number of copies are made rapidly and continuously as recently, the lens must be cleaned at constant intervals. However, to clean the lens, it must be taken out by sliding the dust-proof box off from the clamp member, which is further removed by loosening screws. In short, when dust adhered to the lens has to be cleaned, a complicated and skilled operation is necessitated. Thus, only a special technician familiar with the internal construction of the image forming device is allowed perform such an operation.